Magnetic media are widely used in various applications, particularly in the computer industry, and efforts are continually made with the aim of increasing the areal recording density, i.e., bit density, of the magnetic media. In this regard, so-called “perpendicular” recording media have been found to be superior to the more conventional “longitudinal” media in achieving very high bit densities. In perpendicular magnetic recording media, residual magnetization is formed in a direction perpendicular to the surface of the magnetic medium, typically comprised of a layer of a magnetically “hard” recording material on a suitable substrate. Very high linear recording densities are obtainable by utilizing a “single-pole” magnetic transducer or “head” with such perpendicular magnetic media.
Efficient, high bit density recording utilizing a perpendicular magnetic medium requires interposition of a relatively thick (as compared with the magnetic recording layer), magnetically “soft” underlayer (“SUL”) layer, i.e., a magnetic layer of a ferromagnetic material having a relatively low coercivity below about 1 kOe, such as of a NiFe alloy (Permalloy), between the non-magnetic substrate, e.g., of glass, aluminum (Al) or an Al-based alloy, and the magnetically “hard” recording layer having relatively high coercivity of several kOe, typically about 3-6 kOe, e.g., of a cobalt-based alloy (e.g., a Co—Cr alloy such as CoCrPtB) having perpendicular anisotropy. The magnetically soft underlayer serves to guide magnetic flux emanating from the head through the magnetically hard perpendicular recording layer.
A typical conventional perpendicular recording system 10 utilizing a perpendicular magnetic medium 1 with a relatively thick magnetically soft underlayer, a relatively thin magnetically hard recording layer, and a single-pole head, is illustrated in FIG. 1, wherein reference numerals 2, 2A, 3, 4, and 5, respectively, indicate a non-magnetic substrate, an adhesion layer (optional), a magnetically soft underlayer, at least one non-magnetic interlayer, and at least one magnetically hard perpendicular recording layer. Reference numerals 7 and 8, respectively, indicate the single and auxiliary poles of a single-pole magnetic transducer head 6. The relatively thin interlayer 4 (also referred to as an “intermediate” layer), comprised of one or more layers of non-magnetic materials, serves to: (1) prevent magnetic interaction between the magnetically soft underlayer 3 and the at least one magnetically hard recording layer 5; and (2) promote desired microstructural and magnetic properties of the at least one magnetically hard recording layer.
As shown by the arrows in the figure indicating the path of the magnetic flux φ, flux φ is seen as emanating from single pole 7 of single-pole magnetic transducer head 6, entering and passing through the at least one vertically oriented, hard magnetic recording layer 5 in the region below single pole 7, entering and traveling within soft magnetic underlayer 3 for a distance, and then exiting therefrom and passing through the at least one magnetically hard perpendicular recording layer 5 in the region below auxiliary pole 8 of single-pole magnetic transducer head 6. The direction of movement of perpendicular magnetic medium 1 past transducer head 6 is indicated in the figure by the arrow above medium 1.
With continued reference to FIG. 1, vertical lines 9 indicate grain boundaries of polycrystalline layers 4 and 5 of the layer stack constituting medium 1. Magnetically hard perpendicular recording layer 5 is epitaxially formed on interlayer 4, and while the grains of each polycrystalline layer are of differing widths (as measured in a horizontal direction) represented by a grain size distribution, they are generally in vertical registry (i.e., vertically “correlated” or aligned). Completing the layer stack is a protective overcoat layer 11, such as of a diamond-like carbon (DLC), formed over hard magnetic layer 5, and a lubricant topcoat layer 12, such as of a perfluoropolyethylene material, formed over the protective overcoat layer.
Substrate 2 is typically annular disk-shaped, i.e., with an inner diameter (“ID”) and an outer diameter (“OD”), and comprised of a non-magnetic metal or alloy, e.g., Al or an Al-based alloy, such as Al—Mg having an Ni—P plating layer on the deposition surface thereof, or substrate 2 is comprised of a suitable glass, ceramic, glass-ceramic, polymeric material, or a composite or laminate of these materials. Optional adhesion layer 2A, if present, may comprise an up to about 30 Å thick layer of a material such as Ti or a Ti alloy; soft magnetic underlayer 3 is typically comprised of an about 500 to about 4,000 Å thick layer, typically about 2,000 Å (˜200 nm) thick, of a soft magnetic material selected from the group consisting of Ni, NiFe (Permalloy), Co, CoZr, CoZrCr, CoZrNb, CoFeZrNb, CoFe, Fe, FeN, FeSiAl, FeSiAlN, FeCoB, FeCoC, etc.; interlayer 4 typically comprises an up to about 300 Å thick layer or layers of non-magnetic material(s), such as Ru, TiCr, Ru/CoCr37Pt6, RuCr/CoCrPt, etc.; and the at least one magnetically hard recording layer 5 is typically comprised of an about 100 to about 250 Å thick layer(s) of Co-based alloy(s) including one or more elements selected from the group consisting of Cr, Fe, Ta, Ni, Mo, Pt, V, Nb, Ge, B, and Pd, iron nitrides or oxides, or a (CoX/Pd or Pt)n multilayer magnetic superlattice structure, where n is an integer from about 10 to about 25, each of the alternating, thin layers of Co-based magnetic alloy is from about 2 to about 3.5 Å thick, X is an element selected from the group consisting of Cr, Ta, B, Mo, Pt, W, and Fe, and each of the alternating thin, non-magnetic layers of Pd or Pt is up to about 10 Å thick. Each type of magnetic hard recording layer material has perpendicular anisotropy arising from magneto-crystalline anisotropy (1st type) and/or interfacial anisotropy (2nd type).
According to conventional manufacturing methodology, a majority of the above-described layers constituting perpendicular magnetic recording media are deposited by cathode sputtering, typically by means of multi-cathode and/or multi-chamber sputtering apparatus wherein a separate cathode comprising a selected target material is provided for deposition of each component layer of the stack and the sputtering conditions are optimized for the particular component layer to be deposited. Each cathode comprising a selected target material can be positioned within a respective process sub-chamber or region located within a larger chamber, or in one of a plurality of separate, serially interconnected process chambers each dedicated for deposition of a particular layer. According to such conventional manufacturing technology, a plurality of media substrates, typically in annular disk form, are serially transported by means of a multi-apertured pallet or similar type holder, in linear or circular fashion, depending upon the physical configuration of the particular apparatus utilized, from one sub-chamber or region and/or process chamber to another for sputter deposition of a selected layer thereon.
Sputter deposition of relatively thick component layers of magnetic recording media, particularly the magnetically soft underlayer (SUL) of perpendicular media, in continuous, automatic fashion utilizing the above-described multi-chamber type sputtering apparatus is problematic for the following reasons:
(1) formation of relatively thick media component layers in a single process chamber by means of sputtering utilizing a single sputter deposition source requires a very costly high power, high deposition rate sputtering source to achieve the requisite layer thickness at substrate transport rates consistent with the high product throughput rates necessary for economic competitiveness; and
(2) alternatively, formation of relatively thick media component layers in a single process chamber by means of sputtering utilizing a single, lower power, lower deposition rate sputtering source requires an extremely elongated process chamber and correspondingly extremely elongated sputter deposition source to achieve the requisite layer thickness at substrate transport rates consistent with the high product throughput rates necessary for economic competitiveness.
Approaches for overcoming/avoiding the above-described difficulties and disadvantages in sputter-depositing relatively thick media component layers as part of a continuous, automated manufacturing process at satisfactory product throughput rates and in a cost-effective manner involve forming the relatively thick media component layer, e.g., the magnetically soft underlayer (SUL) of perpendicular magnetic recording media, in several stages or sub-layers, either by means of a plurality of serially arranged sputter deposition sub-chambers or regions located in a single, larger station or chamber of a multi-chamber apparatus, or by means of a plurality of serially arranged sputter deposition stages located in a respective plurality of serially arranged, separate/independent stations or chambers of a multi-chamber apparatus.
However, either of the above approaches entails a disadvantage/drawback in that formation of thick layers of the magnetically soft underlayer material on the shields surrounding the outer periphery (OD) of the annular disk-shaped substrates, eventually leads to flaking-off of the deposited SUL material, with possible deposition of the flaked-off SUL material on the substrate surfaces. This in turn leads to layer defects and reduction in acceptable product yield.
In view of the foregoing, there exists a clear need for means and methodology for manufacturing improved, high areal recording density, high performance perpendicular magnetic recording media, which means and methodology avoid the disadvantages and drawbacks associated with the above-described means and methodology, and which facilitate high throughput, cost-effective, automated manufacture of high performance perpendicular magnetic recording media.
The present invention, therefore, addresses and solves the above-described problems, drawbacks, and disadvantages relating to the poor efficiency and product throughput rates associated with the above-described means and methodology for the manufacture of high performance perpendicular magnetic recording media, while maintaining full compatibility with all aspects of automated magnetic media manufacture.